1. Field of the Invention
The present invention relates to lubricant compositions useful in the working of metals. More particularly, the present invention relates to lubricating fluids useful in plastic deformation processes such as rolling, forging and drawing to offer sufficient lubricity for the materials being worked and the tools being employed and also to provide the worked-products with a beautiful surface finish.
2. Description of the Prior Art
It is well-known that non-soluble oils such as straight mineral, i.e., without an emulsifier, or fatty oils are not completely satisfactory for the working of metals from the standpoint of cooling ability. Thus, emulsion-type lubricants based on mineral or fatty oils have been used conventionally for plastic deformation processes in which a high cooling ability is required in, for example, the hot rolling of aluminium, the manufacturing of aluminium cans by a drawing and ironing process, the cold rolling of steel and so forth. These conventional emulsions contain as an emulsifier, anionic surfactants such as petroleum sulfonates, resin soaps, fatty acid soaps, etc., or nonionic surfactants such as sorbitan alkyl esters, polyoxyethylene sorbitan alkyl esters, etc., having a good cooling ability. However, emulsion-type lubricants have several inherent problems, such as, for example, emulsion stability: the oil droplet sizes of these emulsions tend to increase after some weeks of plant use, particularly in the case of the hot rolling of aluminium, resulting in poor performance, namely the prevalence of uneven lubrication, the removal of oil droplets by filters necessary to remove oxide particles and so forth. Sometimes, in order to obtain a better surface finish on rolled products, emulsion formulations are intentionally designed so that the emulsions are rather unstable. However, this tends to lead to an incidence of refusal at bite. This means that in the case of emulsion-type rolling lubricants, it is somewhat difficult to make a compromise between the surface finish of rolled products and the rollability. Conventional water-soluble lubricating compositions for metal working are disclosed in, for example, U.S. Pat. Nos. 3,492,232, 3,496,104, 3,634,245, etc. However, these prior art water-soluble lubricating compositions are still insufficient, particularly with respect to surface finish characteristics, when they are employed.